I have housesat (for friends & family) and I've also been housesat (by friends & family)... I really don't snoop. I couldn't care less what brand of underwear, or cleaning supplies they use. I do care when I have somebody over to watch my house (usually, it's someone to stop by every other day to feed cats & clean litterboxes). But, it wouldn't matter if somebody was my friend, family, or paid help... I like my house to be as clean as possible when I leave so it's relatively clean when I get back home! The worst is having to ask somebody to take care of pets--especially when it involves cleaning up (scoop dog poop, clean litterbox, wipe up any other miscellaneous messes that my d*mn cats make)! Heck, we had only been in our house for about 5 months when we asked our neighbors to do this for us! We really like them and do trust them with access to our home.
Now, we have people who come over nearly every day to help my brother (speech therapist, physical therapist, and a guy who helps him in the shower), so I am more *aware* of how my house looks. At first, I'd run around like a crazy person before I left every morning to make sure there weren't any dirty dishes (or clothes) lying around. Or, that I hadn't missed a "cat-vomit episode" from the night before... etc, etc. It was crazy! That lasted a few weeks and I finally told myself "screw it! We live here and they are just going to have to ignore our mess when they come over and just do their job!" If they don't like the mess, they are welcome to clean up (ha ha)! I do make sure we don't have anything gross or embarassing left out, though.
If you do trust this person to take care of things (and not steal from you), then I say, do whatever cleaning you would normally do before a trip and just don't worry about the rest (romance books, cleaning supplies, etc)! Enjoy your vacation!!